Antenna, wireless communication device, and electronic device

ABSTRACT

An antenna includes: a substrate on or in which an antenna element part having an open end, a signal line connected to the antenna element part, and a first ground conductor connected to the antenna element part are formed; and a printed wiring board in which a second ground conductor electrically connected to the first ground conductor is formed in a different layer from the first ground conductor, wherein the second ground conductor has a shield part that partially overlaps with the antenna element part including a connection part between the antenna element part and the signal line and a connection part between the antenna element part and the first ground conductor and does not overlap with the open end of the antenna element part when viewed from a normal direction of the printed wiring board.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an antenna, a wireless communicationdevice, and an electronic device.

Description of the Related Art

In recent years, in imaging devices such as digital cameras, and otherelectronic devices, for example, a wireless communication device havinga wireless function is mounted. An electronic device in which a wirelesscommunication device is mounted is able to wirelessly transmit a signalsuch as a captured image to another camera, a personal computer (PC), orthe like by using a wireless Local Area Network (LAN), Bluetooth(registered trademark), or the like. Radio waves of 2.4 GHz, 5 GHz, andthe like are used in a wireless communication by a wireless LAN,Bluetooth (registered trademark), and the like. A wireless communicationdevice may be built into an electronic device or may be installed as anexternal option in an imaging device such as a digital single-lensreflex camera, for example. With installation of such an option in animaging device, it is possible to wirelessly communicate with anotherdevice at a distance of 100 meters or more, for example.

With respect to this type of wireless communication devices, there is aconcern that, when a high power electromagnetic wave emitted from theantenna enters a human body and the energy of the electromagnetic waveis absorbed in the human body, a local rise in temperature may occur inthe human body. It is indicated that such a local rise in temperature ofa human body is likely to increase a risk of development of cataract orthe like, for example. Therefore, in each country, an amount ofabsorption of electromagnetic waves by a human body is evaluated asSpecific Absorption Ratio (SAR), and a regulation value thereof isdefined.

In respect to a technique for suppressing the SAR below a regulationvalue, “Development of Reduction Technology of the Electromagnetic WaveExposure for Biologic Body”, Atsushi Igarashi et al., The Institute ofElectronics, Information and Communication Engineers 2008, Tokyo branchstudent council, a meeting for presenting research papers, Feb. 28,2009, p. 67, B-4 (hereafter, referred to as “Igarashi et al.”) disclosesthat the SAR is inversely proportional to the square of the distancebetween an antenna and a phantom.

Further, Japanese Patent Application Laid-open No. 2005-184703 disclosesthat, for improving the SAR, a part of an electromagnetic wave emittedfrom the antenna element is shielded by a symmetrically structuredground plane adapted to a symmetrically structured antenna element.

According to Igarashi et al., the SAR value can be reduced by putting anantenna away from a human body. In order to put an antenna away from ahuman body, however, it is necessary to secure a larger space between anantenna and an outer casing of an electronic device accommodating theantenna. This results in an increased external size of the electronicdevice and it is therefore difficult to reduce the size or the thicknessof the electronic device including an antenna.

SUMMARY OF THE INVENTION

The present invention intends to provide an antenna, a wirelesscommunication device, and an electronic device that can realize areduction in size and/or thickness of the wireless communication deviceand the electronic device while reducing the SAR value.

An aspect of the present invention provides an antenna including asubstrate on or in which an antenna element part having an open end, asignal line connected to the antenna element part, and a first groundconductor connected to the antenna element part are formed; and aprinted wiring board in which a second ground conductor electricallyconnected to the first ground conductor is formed in a different layerfrom the first ground conductor, wherein the second ground conductor hasa shield part that partially overlaps with the antenna element partincluding a connection part between the antenna element part and thesignal line and a connection part between the antenna element part andthe first ground conductor and does not overlap with the open end of theantenna element part when viewed from a normal direction of the printedwiring board.

Another aspect of the present invention provides a wirelesscommunication device including the above-described antenna.

Further another aspect of the present invention provides an electronicdevice including: the above-described antenna; a communication unit thattransmits or receives a signal via the above-described antenna; and asignal processing unit that processes the signal.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an electronic device accordingto a first embodiment of the present invention.

FIG. 2 is a plan view illustrating an antenna according to the firstembodiment of the present invention.

FIG. 3 is a view schematically illustrating an electromagnetic fielddistribution around the antenna and in a human body.

FIG. 4A, FIG. 4B, and FIG. 4C are views schematically illustratingcurrents flowing in an antenna element part and a magnetic fielddistribution nearby.

FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D are views schematicallyillustrating electric field distributions around the antenna elementpart.

FIG. 6A, FIG. 6B, and FIG. 6C are plan views illustrating calculationmodels of antennae according to an example of the present invention.

FIG. 7 is a perspective view illustrating an arrangement of an antennawith respect to a human body phantom.

FIG. 8 is a graph illustrating calculation results of the SAR values incomparison between the antenna of a first example of the presentinvention and an antenna of a first comparative example.

FIG. 9A is a graph illustrating a calculation result of the SAR valuewhen a size u of a convex part of the antenna of the first example ofthe present invention is changed.

FIG. 9B is a graph illustrating a calculation result of the radiationefficiency when the size u of the convex part of the antenna of thefirst example of the present invention is changed.

FIG. 10 is a graph illustrating a calculation result of the SAR valuewhen a size v of the convex part of the antenna of the first example ofthe present invention is changed.

FIG. 11 is a graph illustrating a calculation result of the SAR valuewhen a size w of the convex part of the antenna of the first example ofthe present invention is changed.

FIG. 12 is a perspective view illustrating an antenna according to asecond embodiment of the present invention.

FIG. 13A, FIG. 13B, and FIG. 13C are views schematically illustratingelectric fields and current distributions on ground conductors for casesof presence and absence of a partially arranged high permittivitymaterial.

FIG. 14A is a graph illustrating a calculation result of the SAR valueof an antenna according to a second example of the present invention.

FIG. 14B is a graph illustrating a calculation result of the radiationefficiency of the antenna according to the second example of the presentinvention.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment

An antenna, a wireless communication device, and an electronic deviceaccording to the first embodiment of the present invention will bedescribed with reference to FIG. 1 through FIG. 11.

FIG. 1 is a perspective view illustrating an electronic device accordingto the present embodiment. FIG. illustrates a digital still camera(hereafter, simply referred to as camera) 10 that is an imaging deviceas the electronic device of the present embodiment. The camera 10 has abuilt-in antenna 101 of the present embodiment and thus has a wirelesscommunication function.

As illustrated in FIG. 1, the camera 10 has a non-conductive outercasing 102, a lens barrel 103 provided in the front side of the outercasing 102, and the antenna 101 of the present embodiment providedinside the outer casing 102.

In the backside in the outer casing 102, a plate-like metal member 104that supports components in the camera 10 is provided. Inside the outercasing 102, a printed circuit board 105 is supported by and fixed to themetal member 104 by screws 106. An image sensor 107 that receives anoptical signal that has passed through the lens barrel 103 and convertsthe received optical signal into an image signal, which is an electricalsignal, is provided on the printed circuit board 105. Further, anintegrated circuit (IC) 108 that processes an image signal generated bythe image sensor 107 is provided on the printed circuit board 105.

Furthermore, a connector 110 is implemented on the printed circuit board105. The connector 110 is electrically connected to the IC 108 through awiring 111 provided in the printed circuit board 105. Further, theantenna 101 of the present embodiment provided inside the outer casing102 is connected to the connector 110 through a cable 109.

The IC 108 is configured to not only function as a signal processingunit that processes image signals and other signals but also function asa communication unit that transmits image signals and transmits andreceives other signals via the antenna 101. The IC 108, which functionsas a communication unit also in such a way, together with the antenna101 form a wireless communication device. For example, the IC 108 canprocess an image signal generated by the image sensor 107 to modulatethe image signal with a frequency in a communication frequency band andwirelessly transmit the modulated signal wave via the antenna 101. As acommunication frequency band, a 2.4 GHz band and a 5 GHz band can beutilized, for example.

The antenna 101 is fixed so as to be located, for example, on an innerside face of the outer casing 102 of the camera in order to increase thedistance from the metal member 104 such that the metal member 104 lessaffects the radio wave radiation of the antenna 101. Note that a fixinglocation of the antenna 101 inside the outer casing 102 is not limitedin particular and can be determined in accordance with a requiredperformance or the like.

FIG. 2 is a plan view illustrating the antenna 101 of the presentembodiment. The antenna 101 of the present embodiment is an inverted Fantenna that is formed of a printed wiring board having at least twowiring layers (conductive layers).

As illustrated in FIG. 2, a plate-like or sheet-like printed wiringboard forming the antenna 101 has at least a first wiring layer 121 thatis a first conductive layer and a second wiring layer 122 that is asecond conductive layer that is different from the first wiring layer121. The first wiring layer 121 and the second wiring layer 122 areformed on or in a plate-like or sheet-like substrate 209 forming adielectric between these layers. For example, in the printed wiringboard forming the antenna 101, the substrate 209 is formed of stackeddielectric layers, and the first wiring layer 121 and the second wiringlayer 122 are formed on the surface of the substrate 209 or inside thedielectric layer forming the substrate 209. Further, for example, theprinted wiring board forming the antenna 101 may be a double-sidedprinted wiring board in which the first wiring layer 121 and the secondwiring layer 122 are formed on one of the surfaces and the other surfaceof the substrate 209, respectively. In FIG. 2, the first wiring layer121 is depicted in the left, and the second layer 122 is depicted in theright.

Inside the outer casing 102 of the camera 10, the antenna 101 isattached to the inner face of a side wall of the outer casing 102 suchthat the first wiring layer 121 is located inside and the second wiringlayer 122 is located outside.

The antenna 101 of the present embodiment, which is an inverted Fantenna, has an antenna element part 201 formed to radiate a magneticwave with a high efficiency at a communication frequency and a signalline 202 electrically connected to the cable 109. The antenna elementpart 201 and the signal line 202 are formed in the first wiring layer121, respectively.

Further, the antenna 101 has ground conductors 203 a and 203 b formed inthe first wiring layer 121, which is on the same layer as the antennaelement part 201, and a ground conductor 204 formed in the second wiringlayer 122, which is on the different layer from the antenna element part201. The antenna 101 further has vias 205 electrically connecting theground conductors 203 a and 203 b to the ground conductor 204.

In the printed wiring board forming the antenna 101, each of the antennaelement part 201, the signal line 202, the ground conductors 203 a, 203b, and 204, and the vias 205 is formed of a conductive material.Further, the substrate 209 that is other than the above components isformed of a dielectric such as a Flame Retardant Type 4 (FR4).

The antenna element part 201, the signal line 202, and the groundconductors 203 a and 203 b formed in the first wiring layer 121 areformed as described below, respectively.

The antenna element part 201 has an L-shaped strip-like planer shape andhas a longer part 201 a that is a first part and a shorter part 201 bthat is a second part. The shorter part 201 b is bent from the longerpart 201 a in a direction orthogonal to the longer part 201 a and isshorter than the longer part 201 a. Note that, although FIG. 2 depictsthe antenna element part 201 having the longer part 201 a and theshorter part 201 b both having a strip-like planer shape with a constantwidth, the planer shape of the antenna element part 201 is not limitedthereto and may be various planer shapes. Further, the direction inwhich the shorter part 201 b is bent is not required to be the directionorthogonal to the longer part 201 a and may be any directionintersecting the longer part 201 a.

The size L that is the total length of the antenna element part 201including the longer part 201 a and the shorter part 201 b is, forexample, one-fourth the wavelength λ of an electromagnetic wave at acommunication frequency in order to emit the electromagnetic wave at ahigh efficiency. Note that FIG. 2 indicates a Cartesian coordinatesystem having an X-axis, a Y-axis, and a Z-axis orthogonal to eachother. In FIG. 2, the longitudinal direction of the longer part 201 a isin a direction parallel to the X-axis. The longitudinal direction of theshorter part 201 b is in a direction parallel to the Y axis. The plateface of the printed wiring board forming the antenna 101 isperpendicular to the direction parallel to the Z-axis. FIG. 1 and FIG.6A, FIG. 6B, FIG. 6C, and FIG. 7 described below represent the sameCartesian coordinate system as FIG. 2.

Further, the antenna element part 201 is electrically connected to thesignal line 202 and the ground conductor 203 a. Note that the antennaelement part 201 is electrically connected to the ground conductor 204and the ground conductor 203 b by connections between the groundconductors 203 a and 203 b and the ground conductor 204 through the vias205 as described later.

One end of the antenna element part 201 in the shorter part 201 b sidewith respect to the size L forms a connection part 201 c to the groundconductor 203 a, and the other end in the longer part 201 a side formsan open end 201 d that is not connected to the ground conductor 203 aand 203 b. Further, in the antenna element part 201, a portion of thelonger part 201 a in the shorter part 201 b side forms a connection part201 e to the signal line 202.

The signal line 202 is formed in a strip-like shape parallel to thelongitudinal direction of the shorter part 201 b in the side to whichthe shorter part 201 b is bent with respect to the longer part 201 a,and is connected to the longer part 201 a at the connection part 201 e.Note that, although FIG. 2 depicts the signal line 202 that has astrip-like planer shape with a constant width, the planer shape of thesignal line 202 is not limited thereto and may be various planer shapes.

The ground conductors 203 a and 203 b that are first ground conductorsare formed in both sides of the signal line 202 such that each of theground conductors 203 a and 203 b has a rectangular planer shape whosepair of sides are parallel to the longitudinal direction of the longerpart 201 a. Note that each of the planer shapes of the ground conductors203 a and 203 b is not limited to a rectangular and may be variousshapes.

The ground conductor 203 a formed in the shorter part 201 b side of thesignal line 202 is connected to the shorter part 201 b at the connectionpart 201 c. That is, the end in the shorter part 201 b side of theantenna element part 201 is connected to the ground conductor 203 a.

In the antenna 101 of the present embodiment, in addition to the groundconductors 203 a and 203 b formed in the first wiring layer 121, theground conductor 204 is formed in the second wiring layer 122 that isdifferent from the first wiring layer 121. The radiation characteristicsof the antenna 101 can be stabilized by the ground conductor 204 beingformed in addition to the ground conductors 203 a and 203 b.Furthermore, this can suppress the variation of radiationcharacteristics among a plurality of the antennae 101 to a smaller levelwhen the plurality of the antennae 101 are manufactured.

The ground conductor 204 formed in the second wiring layer 122 is formedas described below.

The ground conductor 204 that is the second ground conductor is formedso as to have a rectangular portion whose planer shape overlaps with theground conductors 203 a and 203 b correspondingly to the groundconductors 203 a and 203 b formed in the first wiring layer 121.Furthermore, the ground conductor 204 is formed to have a convex part208 protruding toward the antenna element part 201 side from therectangular portion described above. The ground conductor 204 iselectrically connected to the ground conductors 203 a and 203 b via theplurality of vias 205 in rectangular portions overlapping with theground conductors 203 a and 203 b, respectively.

The convex part 208 formed to the ground conductor 204 functions as ashield part that shields a magnetic field as described later. The convexpart 208 is formed so as to have a rectangular planer shape whose pairof sides are parallel to the longitudinal direction of the shorter part201 b, for example. Note that the planer shape of the convex part 208 isnot limited to a rectangular and may be various shapes.

The convex part 208 that functions as a shield part is formed so as topartially overlap with the antenna element part 201 when viewed from thenormal direction of the printed wiring board forming the antenna 101,that is, viewed from the Z-axis direction of FIG. 2. More specifically,the convex part 208 partially overlaps with the antenna element part 201including the connection part 201 e between the signal line 202 and theantenna element part 201 and the connection part 201 c between theground conductor 203 a and the antenna element part 201 when viewed fromthe Z-axis direction. On the other hand, the convex part 208 does notoverlap with the open end 201 d of the antenna element part 201 whenviewed from the Z-axis direction.

In the antenna 101 of the present embodiment, as described above, whenviewed from the Z-axis direction of FIG. 2 that corresponds to thenormal direction of the printed wiring board forming the antenna 101,the convex part 208 which overlaps with a part of the antenna elementpart 201 is formed to the ground conductor 204. The convex part 208 isformed in a region which partially overlaps with the antenna elementpart 201 including the connection part 201 e between the signal line 202and the antenna element part 201 and the connection part 201 c betweenthe ground conductor 203 a and the antenna element part 201 and does notoverlap with the open end 201 d.

Further, as illustrated in FIG. 1 and FIG. 2, the antenna 101 isarranged such that the ground conductors 203 a and 203 b are locatedinside the outer casing 102 and the ground conductor 204 having theconvex part 208 is located outside the outer casing 102. That is, when aparson holds the camera 10, the ground conductor 204 having the convexpart 208 is located closer to the person's body holding the camera 10than the ground conductors 203 a and 203 b.

Because the convex part 208 that partially overlaps with the antennaelement part 201 is formed to the ground conductor 204 as describedabove, the antenna 101 of the present embodiment can reduce the SARvalue, which is a value of the SAR, while suppressing degradation of theradiation characteristics. Moreover, since the antenna 101 of thepresent embodiment is not required to secure a large space between theantenna 101 and the outer casing 102 for reducing the SAR value, areduction in size and/or thickness of the camera 10 can be realized.That is, the antenna 101 of the present embodiment reduces the SARvalue, which is the value of the SAR, while effectively suppressingdegradation of the radiation characteristics by using the component (theground conductor 204) which itself forms the antenna.

In the following, the principle by which the configuration of theantenna 101 of the present embodiment reduces the SAR value whilesuppressing a decrease in the radiation efficiency will be described byusing FIG. 3 through FIG. 5D in this order.

FIG. 3 is a view schematically illustrating an electromagnetic fielddistribution around an inverted F antenna 301 where no convex part 208is formed and in a human body 302 for showing that the magnitude of theSAR value correlates with the magnetic field intensity around anantenna. Description will be provided in comparison with theconfiguration described above for FIG. 2.

The inverted F antenna 301 has an antenna element part 311 correspondingto the antenna element part 201, a signal line 312 corresponding to thesignal line 202, and ground conductors 313 a and 313 b corresponding tothe ground conductors 203 a and 203 b. On the other hand, although theinverted F antenna 301 has a ground conductor (not illustrated)corresponding to the ground conductor 204, this ground conductor isdifferent from the ground conductor 204 in that it has no portioncorresponding to the convex part 208. The inverted F antenna 301 hasvias 315 corresponding to the vias 205 connecting the ground conductorformed in the different wiring layer.

In response to emission of an electromagnetic wave from the inverted Fantenna 301, an electric field 303 and a magnetic field 304 are formednear the inverted F antenna 301 and the human body 302 located near theinverted F antenna 301, respectively. In FIG. 3, the electric field 303is represented by falcate black patterns, and the magnetic field 304 isrepresented by falcate patterns with dashed lines.

First, around the inverted F antenna 301, the electric field 303 ismainly formed near an open end 311 d of the antenna element part 311 dueto a relatively high impedance. On the other hand, the magnetic field304 is mainly formed near a connection part 311 c between the antennaelement part 311 and the ground conductor 313 a due to a relatively lowimpedance.

When the human body 302 approaches the inverted F antenna 301 where theelectric field 303 and the magnetic field 304 are formed as describedabove, the electric field 303 near the inverted F antenna 301 rarelypropagates into the human body 302 and only the magnetic field 304propagates into the human body 302 as illustrated in FIG. 3. The reasonwhy the electric field 303 rarely propagates into the human body 302 isthat the relative permittivity of the human body 302 is as high asapproximately 50 and, when considering an equation of the relationshipbetween an electric flux intensity D and an electric field E, namely,D=εE, the electric field sharply attenuates down to approximately 1/50in the interface between the human body 302 and the air where theelectric flux is continuous. In contrast, the reason why the magneticfield 304 propagates into the human body 302 is that the relativepermittivity of the human body 302 is 1 that is the same as the air and,when considering an equation of the relationship between a magnetic fluxdensity B and a magnetic field H, namely, B=μH, the magnetic field doesnot attenuate in the interface between the human body 302 and the airwhere the magnetic field is continuous.

The magnetic field that has propagated into the human body 302 thenpropagates inside the human body 302 as an electromagnetic wave with anelectric field and a magnetic field due to wavelength shorteningcalculated by an equation, λ=c/(f×the square root of ε_(r)), where λrepresents a wavelength of an electromagnetic wave propagating in amedium, c represents the light velocity in a vacuum, f represents afrequency of an electromagnetic wave propagating in the medium, andε_(r) represents a relative permittivity of the medium. As an example ofwavelength shortening, when the frequency f is 5 GHz and c is 3×10⁸ m/s,the wavelength is calculated to be as low as 8.3 mm inside the humanbody 302, while it is 60 mm in the air.

From the above discussion, it can be seen that what correlates with themagnitude of the SAR value is the magnetic field intensity around theinverted F antenna 301.

FIG. 4A, FIG. 4B, and FIG. 4C are views schematically illustratingcurrents flowing in the antenna element part 201 and magnetic fieldsdistribution nearby for illustrating the principle by which the SARvalue is reduced by the convex part 208 being formed to the groundconductor 204. FIG. 4A and FIG. 4B are sectional views taken along adashed line of an antenna illustrated in FIG. 4C, respectively, and FIG.4A illustrates a case where no convex part 208 is provided and FIG. 4Billustrates a case of the present embodiment where the convex part 208is provided.

In each of the antenna element parts 201 illustrated in FIG. 4A and FIG.4B, since a current flows in a perpendicular direction with respect tothe drawing sheet, a magnetic field is formed in a direction of aright-hand thread as indicated by arrows. As illustrated in FIG. 4A,without the convex part 208, the magnetic field enters a human body 403.In contrast, as illustrated in FIG. 4B, with the convex part 208 beingarranged, the magnetic field is shielded by the convex part 208, so thatthe magnetic field passes between the antenna element part 201 and theconvex part 208, resulting in a reduced SAR value.

In the present embodiment, the convex part 208 partially overlaps withthe antenna element part 201 including the connection part 201 e betweenthe signal line 202 and the antenna element part 201 and the connectionpart 201 c between the ground conductor 203 a and the antenna elementpart 201 when viewed from the Z-axis direction. Thereby, in the presentembodiment, a portion of the antenna element part 201 where a magneticfield is mainly formed is covered with the convex part 208 with respectto a human body located outside the outer casing 102, and therefore amagnetic field that correlates with the SAR value can be effectivelyshielded by the convex part 208. As a result, according to the presentembodiment, the SAR value can be reduced. Further, since the SAR valuecan be reduced by the convex part 208 which itself forms the antenna, itis not necessary to secure a larger space between the antenna 101 andthe outer casing 102.

FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D are views schematicallyillustrating electric field distributions formed around an antennaelement part for illustrating the principle of suppressing a decrease inthe radiation efficiency in a state where the convex part 208 forreducing the SAR value is arranged according to the configuration of theantenna of the present embodiment. FIG. 5A, FIG. 5B, and FIG. 5C areperspective views each depicting only an antenna element part and groundconductors in a dotted line area of the antenna illustrated in FIG. 5D.In FIG. 5A, FIG. 5B, and FIG. 5C, electric fields formed due toradiation of an electromagnetic wave are schematically illustrated byarrows with solid lines. Note that, in FIG. 5A, FIG. 5B, and FIG. 5C,the positional relationship of the antenna element part and the groundconductors is depicted in an inverse manner to that of FIG. 5D for thepurpose of illustration.

Each antenna of the FIG. 5A and FIG. 5B has an antenna element part 501corresponding to the antenna element part 201, ground conductors 503 aand 503 b corresponding to the ground conductors 203 a and 203 b, andvias 505 corresponding to the vias 205. The antenna element part 501 hasa longer part 501 a and a shorter part 501 b corresponding to the longerpart 201 a and the shorter part 201 b, respectively.

FIG. 5A illustrates a case where, instead of the ground conductor 204 ofthe present embodiment, a ground conductor 504 having no convex part 208is formed.

In contrast, FIG. 5B illustrates a case where, differently from theground conductor 204 of the present embodiment, a convex part 508overlapping with an open end 501 d of the antenna element part 501 isformed to the ground conductor 506.

FIG. 5C illustrates a case where the convex part 208 not overlappingwith the open end 201 d of the antenna element part 201 is formed to theground conductor 204 according to the present embodiment.

In the case illustrated in FIG. 5A, the electric field is stronger nearthe open end 501 d of the antenna element part 501 and becomes weaker asapproaching a connection part to the ground conductor 503 a along theantenna element part 501. In the case illustrated in FIG. 5A, since theelectric field is stronger near the open end 501 d of the antennaelement part 501, sufficient radiation efficiency can be obtained.

In contrast, in the case illustrated in FIG. 5B, with the convex part508 being formed overlapping with the open end 501 d of the antennaelement part 501, electric fields formed between the antenna elementpart 501 and the ground conductor 506 are coupled causing a potentialchange. This electric field coupling prevents the radio wave fromradiating from the antenna to the air, which results in a decrease inthe radiation efficiency.

Therefore, in the present embodiment, in order to suppress electricfield coupling described above as much as possible, the convex part 208formed to the ground conductor 204 has a shape that does not overlapwith the open end 201 d as described above. This can suppress a decreasein the radiation efficiency in the present embodiment.

On the other hand, the magnitude of the SAR value correlates with themagnetic field intensity as described above, and a magnetic field ismainly formed near the connection part 201 c between the antenna elementpart 201 and the ground conductor 203 a and the connection part 201 ebetween the antenna element part 201 and the signal line 202. In thepresent embodiment, the convex part 208 is formed to the groundconductor 204 so as to overlap with the connection part 201 c betweenthe antenna element part 201 and the ground conductor 203 a and theconnection part 201 e between the antenna element part 201 and thesignal line 202. Therefore, in the present embodiment, a magnetic fieldcan be shielded by the convex part 208 and thus the SAR value can bereduced. Since the convex part 208 does not overlap with the open end201 d of the antenna element part 201 as described above, a decrease inthe radiation efficiency can be suppressed.

Further, the convex part 208 is not formed of a member separate from theantenna 101 but formed to the ground conductor 204 forming the antenna101. It is therefore unnecessary to provide an additional space forarranging the convex part 208 between the antenna 101 and the outercasing 102. Therefore, the present embodiment can realize a reduction insize and/or thickness of a wireless communication device and anelectronic device having the antenna 101.

As discussed above, the present embodiment can reduce the SAR valuewhile suppressing a decrease in the radiation efficiency. Further,according to the present embodiment, since the SAR value is reduced bythe convex part 208 formed to the ground conductor 204 in the antenna101, it is unnecessary to provide a larger space between the antenna 101and the outer casing 102. Thus, the present embodiment can realize areduction in size and/or thickness of a wireless communication deviceand an electronic device.

FIRST EXAMPLE

Based on the principle described by using FIG. 3, FIG. 4A, FIG. 4B, FIG.4C, FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D, numerical experimentsdescribed below were carried out as an example in order to show that thepresent embodiment can realize a reduction in size and/or thickness of awireless communication device and an electronic device while reducingthe SAR value. In the numerical experiments, the power supplied to theinverted F antenna was 13 dBm, and the communication frequency was 2.45GHz. Further, calculation in the numerical experiments is performed byusing MW-STUDIO that is an electromagnetic simulator from AET, Inc.

FIG. 6A, FIG. 6B, and FIG. 6C are views illustrating calculation modelsof antennae of a first example and a first comparative example ofinverted F antennae each formed of a printed wiring board. FIG. 6Aillustrates a first wiring layer 121 including the antenna element part201 common to the first example and the first comparative example. FIG.6B illustrates a second wiring layer 122′ of the antenna according tothe first comparative example. FIG. 6C illustrates a second wiring layer122 to which the convex part 208 of the antenna is formed according tothe first example. The antenna of the first comparative example is atwo-layered printed wiring board having the first wiring layer 121illustrated in FIG. 6A and the second wiring layer 122′ illustrated inFIG. 6B. The antenna of the first example is a two-layered printedwiring board having the first wiring layer 121 illustrated in FIG. 6Aand the second wiring layer 122 illustrated in FIG. 6C.

In each of the printed wiring boards, the thickness of a wiring was setto 35 and the distance between the layers and the thickness of adielectric of the printed wiring board were set to 0.8 mm. Further, therelative permittivity of the printed wiring board was set to 4.3expecting the FR4, and the dielectric loss tangent tans was set to0.025.

FIG. 7 illustrates a calculation model when outputting the SAR value. Asdepicted, a human body phantom 701 and the antenna 101 of the firstexample or an antenna 101′ of the first comparative example are arrangedsuch that all the faces thereof are parallel to each other. The distancefrom the human body phantom 701 to the second wiring layer 122′ of theantenna 101′ (FIG. 6B) or the distance from the human body phantom 701to the second wiring layer 122 (FIG. 6C) was x mm. Table 1 illustratessizes a to w and the distance x depicted in FIG. 6A, FIG. 6B, FIG. 6C,and FIG. 7. Note that the values u to x of the sizes a to w and thedistance x are variables.

TABLE 1 size and distance [mm] of calculation model symbol a b c d e f gh i j size 5.3 41.775 0.85 3.0 25.025 17.975 2.5 24.425 26.475 10.2 [mm]symbol k 1 m n o p q r s t size 49.975 50.9 8.5 1.0 49.05 2.4 3.25 4.72.35 19.8 [mm] symbol u v w x size variable variable variable variable[mm]

For calculation of the SAR value, a material constant of a solvent of ahuman body phantom used in measurement according to the internationalstandard was used, and the conductivity σ was 2 S/m, the relativepermittivity was 52.21, the tan δ was 0.28, the physical density ρ was1000 kg/m³. The SAR value was obtained by measuring the electric field Einside the human body phantom and calculating the SAR value according toan equation expressed by:

SAR value [W/kg]=E×E×ρ/σ.

With respect to the communication characteristics, the radiationefficiency was calculated in a state where the human body phantom wasremoved. The radiation efficiency was obtained by calculating a ratio ofpower supplied to the signal line at the communication frequency and thetotal power of radiated electromagnetic waves passing through points ata distance of 1 m from the antenna as the center.

FIG. 8 illustrates calculation results of the SAR values in comparisonbetween the antenna of the first example and the antenna of the firstcomparative example. In FIG. 8, the dashed line represents a calculationresult for the antenna of the first comparative example, and the solidline represents a calculation result for the antenna of the firstexample. In the antenna of the first example here, v=9.1, u=20, andw=10.925 were applied for the sizes v, u, and w of the convex part 208formed to the ground conductor 204.

As illustrated in FIG. 8, it can be seen that an increase in the valueof the distance x between the second wiring layer of the antenna and thehuman body phantom results in a decrease in the SAR value in both casesof the first example and the first comparative example. In comparison ofthe distance x at which the SAR value decreases below 1.6 W/kg that is astandard value of the SAR value, while the distance x at which the SARvalue is 1.6 W/kg is x=6.5 mm in the antenna of the first comparativeexample, it is x=4.5 mm in the first example. This result shows that thefirst example allows for a reduction in the thickness, namely, thedistance from the antenna to the outer casing down to approximatelytwo-thirds the thickness of the first comparative example.

FIG. 9A and FIG. 9B illustrate calculation results of the SAR value andthe radiation efficiency with respect to the antenna of the firstexample when the value of the size u of the convex part 208 is changed,FIG. 9A illustrates a calculation result of the SAR value, and FIG. 9Billustrates a calculation result of the radiation efficiency. In thecalculation, the distance x from the second wiring layer of the antennato the human body phantom was fixed to x=4 mm, and the sizes v and w ofthe convex part 208 formed to the ground conductor 204 were fixed tov=9.1 and W=10.925. For the convex part 208 determined by these sizes,the relationship of the sizes a, f, g, and w illustrated in FIG. 6A,FIG. 6B, and FIG. 6C meets f>w and a+g<v. Thus, the convex part 208overlaps with a part of the antenna element part 201 and the connectionpart 201 c between the antenna element part 201 and the ground conductor203 a when viewed from the Z-axis direction.

The value u=8.2 is a value when one end of the convex part 208 overlapswith the open end 201 d of the antenna element part 201. The valueu=24.1 is a value when the one end of the convex part 208 overlaps withthe signal line 202. Note that the one end of the convex part 208 means,of the ends in the X-axis direction of the convex part 208, an end inthe open end 201 d side of the antenna element part 201.

As illustrated in FIG. 9A, it can be seen that the SAR value decreaseswhen u≤24.1, that is, when the antenna element part 201 is covered withthe convex part 208 by a larger area than a region covering theconnection part 201 e connected to the signal line 202. Thus, in orderto allow for a reduction in size and/or thickness, the convex part 208is required to cover the connection part 201 e connected to the signalline 202 that is a power supply part of the antenna element part 201.

Further, the SAR value is the minimum when u=10, and the SAR value ismaintained low in the range of u<10 even when the value u is changed andthere is no change in the effect of a reduction in size and/orthickness. In the first example, the length corresponding to the size Lof the antenna element part 201 is calculated to be 28.85 mm based onFIG. 6A, FIG. 6B, and FIG. 6C. Therefore, the value of u=10 is a valuewhen the distance from the open end 201 d of the antenna element part201 to the one end of the convex part 208 is around 2 mm, which isaround one-tenth the size L of the antenna element part 201.

It is therefore preferable that the size u of the convex part 208 begreater than or equal to a value where the distance from the open end201 d of the antenna element part 201 to the one end of the convex part208 is one-tenth the size L of the antenna element part 201 and be lessthan or equal to a value where the one end of the convex part 208overlaps with the signal line 202. That is, the one end of the convexpart 208 is preferably located between the position where the distancefrom the open end 201 d is one-tenth the size L of the antenna elementpart 201 and the position that overlaps with the signal line 202. Thatis, the one end of the convex part 208 is preferably located in aposition between the point where the distance from the open end 201 d ofthe antenna element part 201 is one-tenth the size L and the connectionpart 201 e between the antenna element part 201 and the signal line 202when viewed from the normal direction of the printed wiring board.

On the other hand, as illustrated in FIG. 9B, it can be seen that, in asimilar manner to the reduction of the SAR value, the radiationefficiency decreases as the value u decreases from the value in u≤24.1.The relationship between a reduction effect of the SAR value and theradiation efficiency with respect to the size of the convex part 208will be described below.

According to calculation for the antenna of the first comparativeexample without the convex part 208, in a case of the distance x=4 mm,the SAR value is 2.2 W/kg and the radiation efficiency is −0.27 dB,which means that 98% of the supply power input from the signal line 202is radiated.

In contrast, based on FIG. 9A and FIG. 9B, it is when u=20 thatformation of the convex part 208 causes the SAR value to decrease to thestandard value 1.6 W/kg, namely, to 72%. The radiation efficiency inthis case is reduced to −2.2 dB, namely, by 39%, which means that 60% ofthe supply power input from the signal line is radiated. Furthermore, itis when u=18 that formation of the convex part 208 causes the SAR valueto decrease to the standard value 1.1 W/kg, namely, decrease by half.The radiation efficiency in this case is reduced to −3.7 dB, namely, by57%, which means that 42% of the supply power input from the signal lineis radiated.

In such a way, the relationship between a reduction effect of the SARvalue and the radiation efficiency with respect to the size of theconvex part is a tradeoff relationship. Therefore, in practice, the sizeof the convex part can be determined by a desired reduction amount ofthe SAR value and a desired radiation efficiency.

Next, based on the principle of FIG. 3, it will be shown that, with theconvex part 208 covering the connection part 201 e between the antennaelement part 201 and the signal line 202 and the connection part 201 cbetween the antenna element part 201 and the ground conductor 203 awhere the magnetic field intensity is high, there is no influence on thereduction characteristics of the SAR value. To this end, calculationsimilar to that illustrated in FIG. 9A and FIG. 9B is carried out withchanges of the sizes v and w of the convex part. FIG. 10 and FIG. 11illustrate calculation results.

FIG. 10 illustrates a calculation result of the SAR value obtained bychanging the value of the size u when the size v of the convex part 208was changed from 9.1 mm to 13 mm, the solid line represents the case ofv=13 mm, and the dashed line represents the case of v=9.1 mm. In asimilar manner to the case of v=9.1 mm, the case of v=13 mm correspondsto a state where the convex part 208 covers the connection part 201 ebetween the antenna element part 201 and the signal line 202 and theconnection part 201 c between the antenna element part 201 and theground conductor 203 a. It can be seen from FIG. 10 that, with theconvex part 208 covering the connection parts 201 e and 201 c, there isno influence on the reduction characteristics of the SAR value even whenthe size v is changed.

FIG. 11 illustrates a calculation result of the SAR value obtained bychanging the value of the size u when the size w of the convex part 208was changed from 10.925 mm to 14.925 mm, the solid line represents thecase of w=14.925 mm, and the dashed line represents the case of w=10.925mm. In a similar manner to the case of w=10.925 mm, the case of v=14.925mm corresponds to a state where the convex part 208 covers theconnection part 201 e between the antenna element part 201 and thesignal line 202 and the connection part 201 c between the antennaelement part 201 and the ground conductor 203 a. It can be seen fromFIG. 11 that, with the convex part 208 covering the connection parts 201e and 201 c, there is no influence on the reduction characteristics ofthe SAR value even when the size w is changed.

Note that, although the convex part 208 in the antenna of the firstexample has a rectangular planer shape defined by the sizes u, v, and w,the planer shape of the convex part 208 may be other shapes.

Second Embodiment

An antenna, a wireless communication device, and an electric device ofthe second embodiment of the present invention will be described byusing FIG. 12 to FIG. 14B. Note that the same components as those in theantenna of the first embodiment are labeled with the same referencenumerals as those in the first embodiment, and the description thereofwill be omitted or simplified.

The first embodiment and the first example described above have shownthat the SAR value is reduced by forming the convex part 208 that islocated between the antenna element part 201 and the human body andformed to the ground conductor 204 formed in a wiring layer differentfrom the antenna element part 201 to cover the antenna element part 201.As a result, it is possible to put the antenna element part 201 close toa human body, which allows for a reduction in size and/or thickness ofthe external dimensions of a wireless communication device and anelectronic device.

The present embodiment and a second example described later will showthat the reduction amount of the SAR value is increased by a highpermittivity part made of a high permittivity material partiallyarranged to the antenna of the first embodiment and the first example,which allows for a further reduction in size and/or thickness of awireless communication device and an electronic device.

FIG. 12 is a perspective view illustrating an antenna of the presentembodiment. An antenna 1101 of the present embodiment is similar to theantenna of the first embodiment except that a high permittivity part1201 made of a high permittivity material is partially arranged to theantenna of the first embodiment described above.

As illustrated by the dashed line in FIG. 12, the high permittivity part1201 whose relative permittivity is higher than other parts is providedin the substrate 209. The high permittivity part 1201 is arrangedbetween the first wiring layer 121 and the second wiring layer 122 so asto overlap with the convex part 208. In the case illustrated in FIG. 12,the high permittivity part 1201 is arranged so as to overlap with theentire convex part 208. Note that the high permittivity part 1201 is notrequired to overlap with the entire convex part 208 and may also bearranged partially overlapping with the convex part 208. The highpermittivity part 1201 may be provided in at least a predeterminedregion on the convex part 208. The predetermined region in this contextis a region where the antenna element part 201 including the connectionpart 201 e and the connection part 201 c partially overlaps with theconvex part 208 when viewed from the normal direction of the printedwiring board.

The high permittivity part 1201 is a portion whose relative permittivityis higher than other portions of the substrate 209 in the printed wiringboard forming the antenna 1101. The high permittivity material of thehigh permittivity part 1201 is, for example, a ceramics material whoserelative permittivity is higher than or equal to 28 and lower than orequal to 32 and is higher than the relative permittivity of a dielectricof the substrate 209. For example, a BaO—TiO₂—ZnO-based ceramicsmaterial can be used as the high permittivity material of the highpermittivity part 1201.

Note that the high permittivity part 1201 can be formed, for example, bymechanically machining a part of the substrate 209 of the printed wiringboard forming the antenna 1101 and arranging the high permittivitymaterial in the machined part. Alternatively, for example, an electroniccomponent that is implemented between different wiring layers of theprinted wiring board and has a built-in component made of ceramicsmaterial may be utilized as the high permittivity part 1201.

The antenna 1101 of the present embodiment may be built into the camera10 and form a wireless communication device together with the IC 108 ina similar manner to the case of the first embodiment.

The fact that the reduction amount of the SAR value is increased by thehigh permittivity part 1201 being arranged will now be described byusing FIG. 13A, FIG. 13B, and FIG. 13C. As illustrated by using FIG. 3,FIG. 4A, FIG. 4B, and FIG. 4C, the SAR value is reduced in the firstembodiment by using the convex part 208 to suppress the transmissionamount of a magnetic field formed by the antenna 101 into a human body.However, the convex part 208 is formed so as not to overlap with theopen end 201 d of the antenna element part 201 in order to suppress adecrease in the radiation efficiency. The structure in which the convexpart 208 does not overlap with the open end 201 d causes an electricfield to be formed between the open end 201 d and the ground conductors203 b and 204 as illustrated in FIG. 5C. After coupling to the groundconductors 203 b and 204, this electric field causes a return currentflowing on the ground conductors 203 b and 204 and forms a loop betweenthe antenna element part 201 and the ground conductors 203 b and 204.

The current flowing in the ground conductor 204 may cause an increase inthe SAR value, because the ground conductor 204 is located in the humanbody side and thus a magnetic field formed by this current propagatesinto the human body.

FIG. 13A schematically illustrates a current flowing on the surface ofthe ground conductor 204 in the human body side in the case illustratedin FIG. 5C. FIG. 13A schematically illustrates a current by arrows withdashed lines. As illustrated in FIG. 13A, the return current flows overa wide area of the ground conductor 204 through the vias 205 as pathsdepending on a region where the electric field is coupled.

FIG. 13B schematically illustrates an electric field of the same regionas in FIG. 5C when the high permittivity part 1201 illustrated in FIG.12 is arranged. In FIG. 13B, the electric field formed at radiation ofelectromagnetic waves is schematically illustrated by arrows with solidlines. As illustrated in FIG. 13B, the arrangement of the highpermittivity part 1201 in a region overlapping with the convex part 208allows an electric field to be formed in the convex part 208 side andformed closer to a space between the ground conductor 203 b and theground conductor 204 compared to the case illustrated in FIG. 5C. Thisresults in a reduction of the electric field area that would otherwisebe formed in a wide area between the open end 201 d and the groundconductor 203 b.

FIG. 13C schematically illustrates a current flowing on the surface ofthe ground conductor 204 in the human body side in the case illustratedin FIG. 13B. FIG. 13C schematically illustrates a current by arrows withdashed lines. As illustrated in FIG. 13C, the arrangement of the highpermittivity part 1201 reduces the amount of a current flowing on thesurface of the ground conductor 204 in the human body side. This allowsfor a further reduction of the magnetic field propagating in a humanbody and therefore a further reduction of the SAR value.

As discussed above, in the present embodiment, the arrangement of thehigh permittivity part 1201 increases the amount of the reduction of theSAR value compared to the first embodiment, which allows for a furtherreduction in size and/or thickness of the external dimensions of awireless communication device.

SECOND EXAMPLE

Based on the principle described above, numerical experiments describedbelow were carried out as an example. In the numerical experiments, arectangular parallelepiped region defined by the size v, the size(k-u-w), and 0.8 mm, which is the thickness of the dielectric, isprovided to the calculation model illustrated in FIG. 6A, FIG. 6B, andFIG. 6C. The SAR value and the radiation efficiency value werecalculated for the condition where the relative permittivity of onlythis region was changed without changing the relative permittivity ofother regions from 4.3. The sizes were set as u=20, w=10.925, k=49.975,v=9.1, and (k-u-w)=19.05. Further, the distance x was 4 mm. Note thatcalculation conditions were the same as the cases illustrated in FIG.6A, FIG. 6B, FIG. 6C, and FIG. 7 of the first example, the powersupplied to the inverted F antenna was 13 dBm, and the communicationfrequency was 2.45 GHz. Further, calculation in the numericalexperiments is performed by using MW-STUDIO that is an electromagneticsimulator from AET, Inc.

FIG. 14A and FIG. 14B illustrate calculation results of the SAR valueand the radiation efficiency, respectively. In FIG. 14A and FIG. 14B,the solid line represents a result when only the relative permittivityof the above-described region defined by the size v and the size (k-u-w)overlapping with the convex part 208 is changed. For reference, in FIG.14A and FIG. 14B, the dashed lines represent a calculation result whenthe relative permittivity of a region of a rectangular parallelepiped ofthe open end 201 d side, that is, a region defined by the size v, thesize u, and 0.8 mm, which is the thickness of the dielectric, is changedand the relative permittivity of other regions is not changed from 4.3.

First, as illustrated by the solid lines of FIG. 14A and FIG. 14B, infocusing on values where the relative permittivity is approximately 28to 32 in comparison with the case where the relative permittivity is4.3, it can be seen that the SAR value decreases from 1.6 W/kg to 1.2W/kg while the radiation efficiency does not change significantly. Thecase where the relative permittivity is 4.3 corresponds to the casewhere the high permittivity part 1201 is not arranged. With the highpermittivity part 1201 being arranged to the region of the convex part208, the second example can reduce the size and/or the thickness tothree-fourths that of the first example.

On the other hand, as illustrated in the dashed lines in FIG. 14A andFIG. 14B, the SAR value decreases when the high permittivity part madeof a high permittivity material is partially provided in the open end201 d side only of the antenna element part 201. Therefore, in thiscase, the advantage of the reduction in size and/or thickness is notobtained.

The reason why the SAR value decreases when a high permittivity part ispartially provided only in the open end 201 d side of the antennaelement part 201 is as follows. In this case, an electric field is notformed as illustrated above by using FIG. 13B but formed in the open end201 d side of the antenna element part 201 and formed close to a spacebetween the ground conductor 203 b and the ground conductor 204. As aresult, the amount of a current flowing on the surface of the groundconductor 204 in the human body side becomes larger than that in thecase illustrated in FIG. 13A and therefore the SAR value decreases.

As a result of an electric field is formed closer to the open end 201 dside of the antenna element part 201, however, the radiation efficiencyis improved. Thus, a partial arrangement of a high permittivity part inthe open end 201 d side of the antenna element part 201 allows for theadvantage of reduced supply power for the same SAR value or the sameexternal dimensions of the wireless communication device. Therefore, forthe purpose of reducing supply power, a high permittivity part may bepartially arranged in the open end 201 d side of the antenna elementpart 201.

Note that, when the relative permittivity of the substrate 209 made ofthe dielectric illustrated in FIG. 6A, FIG. 6B, and FIG. 6C is entirelychanged rather than partially changed, no change occurs in the formationof an electric field. Thus, there will be only a slight change in theSAR value and the radiation efficiency, and the advantage of a reducedsize and/or thickness or reduced supply power is not obtained.

Modified Embodiment

The present invention is not limited to the embodiments described above,and various modifications are possible.

For example, although a digital still camera that is an imaging devicehas been exemplified as an electronic device having a wirelesscommunication function in the above-described embodiment, an electronicdevice is not limited thereto. An electronic device having a wirelesscommunication function may be a communication terminal such as a mobilephone, a smartphone, or the like, a personal computer (PC) such as anotebook PC, a tablet PC, in addition to the imaging device such as adigital still camera, a digital video camera, or the like. An electronicdevice according to one embodiment of the present invention can beconfigured to have an antenna according to the embodiments describedabove, a communication unit that transmits and receives a signal via theantenna, and a signal processer that processes the signal.

Further, although the above-described embodiments have exemplified acase where the antenna 101 is built into the camera 10 that is anelectronic device, and the IC 108 and the antenna 101 built into thecamera 10 form a wireless communication device, the wirelesscommunication device is not limited thereto. The wireless communicationdevice according to the embodiments of the present invention may alsohave an antenna according to the embodiments described above and acommunication unit that transmits and receives a signal via the antennaand may be configured to be used in connection with an electronicdevice.

Further, although the above-described embodiments have exemplified acase where the antenna element part 201, the signal line 202, and theground conductors 203 a and 203 b are formed in the same layer of thefirst wiring layer 121, the arrangement is not limited thereto. Theantenna element part 201, the signal line 202, and the ground conductors203 a and 203 b may be formed in different wiring layers. In this case,the antenna element part 201 and the signal line 202 may be electricallyconnected through one or more vias, and the antenna element part 201 andthe ground conductor 203 a may also be electrically connected throughone or more vias.

Further, although the inverted F antenna has been exemplified as anantenna in the above-described embodiments, an antenna is not limitedthereto, and the present invention is applicable to various types ofantennae.

According to the embodiments of the present invention, a reduction insize and/or thickness of a wireless communication device and anelectronic device can be realized with a reduction of the SAR value.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2016-009751, filed Jan. 21, 2016, which is hereby incorporated byreference herein in its entirety.

1.-9. (canceled)
 10. A wireless communication device comprising ahousing and an antenna, wherein: the antenna is arranged inside thehousing, the antenna has a first layer and a second layer, the firstlayer is comprised of an antenna element part having an open end, asignal line connected to the antenna element part, and a first groundconductor connected to the antenna element part, the second layer iscomprised of a second ground conductor electrically connected to thefirst ground conductor, and the second ground conductor overlaps with aconnection part between the antenna element part and the signal line anda connection part between the antenna element part and the first groundconductor and does not overlap with the open end of the antenna elementpart when viewed from a normal direction of the first layer.
 11. Thewireless communication device according to claim 10, wherein the secondlayer is arranged at a position nearer the housing than the first layerinside the housing.
 12. The wireless communication device according toclaim 10, wherein: the antenna is a printed wiring board comprised of asubstrate, and the first layer and the second layer are formed on or inthe substrate.
 13. The wireless communication device according to claim10, wherein: the antenna element part has a first part and a second partbent from the first part, the connection part between the antennaelement part and the first ground conductor is an end of the secondpart, and the signal line is connected to the first part.
 14. Thewireless communication device according to claim 10, wherein the lengthof the antenna element part, which does not overlap with the secondground conductor when viewed from the normal direction of the firstlayer, from the open end of the antenna element is more than one-tenththe total length of the antenna element part and less than the lengthfrom the open end of the antenna element to the connection part betweenthe antenna element part and the signal line.
 15. The wirelesscommunication device according to claim 10, wherein: the substrate has ahigh permittivity part whose relative permittivity is higher than otherparts, and the high permittivity part is provided in a region where theconnection part between the antenna element part and the signal line andthe connection part between the antenna element part and the firstground conductor overlap with the shield part when viewed from thenormal direction of the printed wiring board.
 16. The wirelesscommunication device according to claim 15, wherein a relativepermittivity of the high permittivity part is higher than or equal to 28and lower than or equal to
 32. 17. The wireless communication deviceaccording to claim 16, wherein a dielectric of the high permittivitypart is a ceramics material.
 18. An electronic device comprising: thewireless communication device according to claim 10; and a signalprocessing unit that processes a signal for transmit to the wirelesscommunication device or the signal received by the wirelesscommunication device.
 19. The electronic device according to claim 18,wherein the second ground conductor has a shield part, and the shieldpart is arranged at a position nearer the housing than the antennainside the housing.
 20. The electronic device according to claim 18,wherein electronic device is a camera.
 21. A wireless communication unitcomprising an antenna, wherein: the antenna has a first layer and asecond layer, a first layer is comprised of an antenna element parthaving an open end, a signal line connected to the antenna element part,and a first ground conductor connected to the antenna element part, asecond layer is comprised of a second ground conductor electricallyconnected to the first ground conductor, and the second ground conductoroverlaps with a connection part between the antenna element part and thesignal line and a connection part between the antenna element part andthe first ground conductor and does not overlap with the open end of theantenna element part when viewed from a normal direction of the firstlayer.
 22. A wireless communication device comprising a housing and anantenna, wherein: the antenna is arranged inside the housing, theantenna is a printed wiring board comprised of a substrate and aplurality of layers, the antenna has an antenna element part having anopen end, a signal line connected to the antenna element part, and afirst ground conductor connected to the antenna element part, a secondground conductor electrically connected to the first ground conductor,and the second ground conductor overlaps with a connection part betweenthe antenna element part and the signal line and a connection partbetween the antenna element part and the first ground conductor and doesnot overlap with the open end of the antenna element part when viewedfrom a normal direction of the printed wiring board.